Synthesis of gold nanoparticles using red algae extract

ABSTRACT

A method for preparing gold metal nanoparticles, e.g., nanospheres and nanoprisms, includes combining an extract of red algae with chloroauric acid (HAuCl 4 ). The red algae can be  Laurencia papillosa . The extract can include a water solvent extract. The chloroauric acid (HAuCl 4 ) can be in an aqueous solution. The method can include providing chloroauric acid 
     (HAuCl 4 ), providing a red algae extract, and combining the chloroauric acid (HAuCl 4 ) and the red algae extract to produce gold nanoparticles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to nano-biotechnology, and particularly, to the synthesis of gold nanoparticles using red algae extract as a reducing agent.

2. Description of the Related Art

Nanoparticles exhibit completely new or improved properties compared to their corresponding bulk materials. Because of their size, catalytic property, ability to deliver drug, increased efficacy, and decreased toxicity, nanotechnology finds applications in various fields including healthcare, defense, and day-to-day life. Because the nanoparticles possess a very high surface to volume ratio, they are particularly useful in applications where high surface areas are critical for success.

The green synthesis of eco-friendly nanoparticles is of great interest in nanoscience for biomedical applications and specifically for clinical applications. Gold nanoparticles (GNPs), especially nano-prisms, represent an important tool for studying cell function, for use in optoelectronics, in delivery systems for controlling plant virus diseases, and in nanomedicine.

Conventional physical and chemical methods for the synthesis of metal nanoparticles are typically expensive and require the use of toxic and aggressive chemicals. It would be desirable to produce gold metal nanoparticle utilizing a rapid, low cost, ecofriendly “green” method.

Thus, a method of synthesizing noble metal nanoparticles utilizing red algae extract as a reducing agent solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

A method for preparing gold metal nanoparticles, e.g., nanospheres and nanoprisms, includes combining an extract of red algae with chloroauric acid (HAuCl₄). The red algae can include Laurencia papillosa. The extract can be a water solvent extract. The method can include providing a solution of chloroauric acid (HAuCl₄), providing an aqueous red algae extract solution, and combining the solution of chloroauric acid (HAuCl₄) and the red algae plant extract solution while stirring at room temperature to produce gold nanoparticles. The nanoparticles can include nanospheres and/or nanoprisms, depending on the concentration of chloroauric acid (HAuCl₄) used. In some embodiments, the nanoparticles can include nanospheres, which are converted into nanoprisms. The gold nanoparticles can have a mean diameter in the range of from about 3.5 nm to about 53.5 nm.

These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the UV-Vis spectra for the gold nanoparticles synthesized using different concentrations of tetrachloroauric acid (HAuCl₄).

FIG. 2 is a graph showing the concentration of tetrachloroauric acid (HAuCl₄) versus the size of the gold nanoparticles synthesized by the method of the invention.

FIGS. 3A is a graph showing the gray scale versus distance plot profile for the triangular nanoprism structures.

FIG. 3B is a graph showing the gray scale versus distance plot profile for the truncated hopper structures.

FIGS. 4A is a graph showing the atomic force microscopy (AFM) counts versus distance plot profile for the triangular structures.

FIG. 4B is a graph showing the counts versus distance atomic force microscopy (AFM) plot profile for the truncated hopper structures.

FIG. 5 is a graph showing the representative X-ray diffraction (XRD) pattern of the synthesized gold nanoparticles.

FIG. 6 is a graph showing the FTIR spectra of Laurencia papillosa extract and the as synthesized gold nanoparticles.

FIG. 7 is a graph showing the X-ray photoelectron spectroscopy (XPS) spectrum of the as synthesized gold nanoparticles.

Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method for preparing gold metal nanoparticles, e.g., nanospheres and nanoprisms, includes combining an extract of red algae with chloroauric acid (HAuCl₄). The red algae can be Laurencia papillosa. The extract can include a water solvent extract. The chloroauric acid (HAuCl₄) can be in an aqueous solution. The method can include providing chloroauric acid (HAuCl₄), providing a red algae extract, and combining the chloroauric acid (HAuCl₄) and the red algae extract to produce a solution including gold nanoparticles. Combining the chloroauric acid (HAuCl₄) and the red algae extract can include stirring at room temperature. The nanoparticles can include nanospheres and/or nanoprisms, depending on the concentration of chloroauric acid (HAuCl₄) used. In some embodiments, the nanoparticles can include nanospheres, which are converted into nanoprisms.

The solution of chloroauric acid (HAuCl₄) can have a concentration of, for example, about 0.25 mM to about 5.0 mM (HAuCl₄). The concentration of the red algae extract can range from about 0.01 g/mol to about 0.10 g/mol. Preferably, the concentration of the red algae extract is about 0.05 g/mol. Typically, the resulting gold nanoparticles can have a mean diameter in the range of from about 1 nm to about 100 nm and preferably from about 3.5nm to about 53.5 nm. The gold nanoparticles can be spherical, spheroidal, elongated spherical, faceted, or prismatic. While gold nanoparticles are described herein, it should be understood that other metal nanoparticles can be synthesized by combining a metal ion solution and the red algae plant extract solution, as described above.

Preparing an extract of red algae can include pulverizing a quantity of dried red algae samples into small pieces; boiling the pieces in water for about 5 to 10 minutes to provide a boiled extract solution; and isolating the extract using conventional methods, e.g., centrifugation at 5000 rpm for about five minutes at a temperature of 5° C. and separating the centrifuged pellet from the supernatant which is Pure Algal Extract (PAE). Gold nanoprisms and other desired morphologies can be achieved in this one-step reaction simply by varying the concentration (molarity) of chloroauric acid (HAuCl₄), as described in the examples below.

As used herein, the term “Nanoparticle” refers to a particle having at least one dimension sized between 1 and 100 nanometers. The metal nanoparticles described herein can be gold nanoparticles. The gold nanoparticles can be from about 1 nm to about 100 nm in diameter, and preferably from about 3 nm to about 55 nm in diameter. The metal nanoparticles can include nanospheres and/or nanoprisms.

The method of producing gold nanoparticles using the extract of red algae is a green, simple, low cost, ecofriendly and affordable method, which can easily be scaled up for large scale synthesis. The nanoparticles can have applications in drug delivery, nanomedicine, e.g., diagnostic applications, as well as optoelectronics. The following examples will further illustrate the synthesis of gold nanospheres and nano-prisms using red algae.

Example 1 Green Synthesis of Gold Nanoparticles Using Laurencia papillosa

Samples of Laurencia papillosa were collected, and then washed with fresh water repeatedly. Samples were air dried in the shade for 5 days, then ground into small pieces. Five grams of the dried samples were boiled in 100 ml sterile water for 5 minutes. The boiled extract solution was centrifuged at 5000 rpm for 5 minutes at 5° C. The centrifuged pellet was discarded and the supernatant pure algal extract (PAE) was used for the synthesis of gold nanoparticles (GNPs). The GNPs were produced in a one-step reaction, in which the supernatant pure algal extract (PAE) was combined with chloroauric acid (HAuCl₄). A concentration of about 0.05 g/mol of the red algae extract was reacted separately with different concentrations of chloroauric acid (HAuCl₄), with each reaction having a total final volume of 4 ml. The UV-Vis spectra of the GNP's synthesized using the different chloroauric acid (HAuCl₄) concentrations (0.25 mM, 0.50 mM, 1.0 mM, 2.0 mM, 3.0 mM, 4.0 mM, and 5.0 mM), are shown in FIG. 1. The PAE volume and concentration were kept constant at room temperature. The color of the reaction mixture changed into ruby indicating the synthesis of the gold nanoparticles (GNPs) with sizes that varied from 3.5 nm to 53.5 nm. FIG. 2 shows the size of the gold nanoparticles as a function of the concentration of Chloroauric acid (mM), indicating that the size increases with use of higher chloroauric acid (AuCl₄) concentration.

The synthesized gold nanoparticles were characterized by several physico-chemical techniques. TEM images revealed gold nanoparticles of different shapes and sizes, varying from uniform gold nanospheres to nanotriangular prisms, depending on the concentration of chloroauric acid (mM) used. The nanoprisms were single crystalline structures, whose basal plate surface are atomically flat “111” planes. For chloroauric acid (HAuCl₄) concentrations of 0.25 mM, 0.50 mM, and 1.0 mM, the nanoparticles were generally gold nanospheres. Initial induction of gold nanospheres into gold nanoprisms was noted when a chloroauric acid (HAuCl₄) concentration of 2.0 mM was used. At chloroauric acid (HAuCl₄) concentrations of 3.0 mM, 4.0 mM, significant growth of gold nanoprisms was noted. When a chloroauric acid (HAuCl₄) concentration of 5.0 mM was used, fully formed gold nanoprism structures were observed. FESEM images revealed two types of nanoprism structures: flat, triangular structures and truncated, hopper structures.

FIG. 3A shows the gray scale versus distance plot profile for the triangular nanoprism structures. FIG. 3B shows the gray scale versus distance plot profile for the truncated hopper structures. FIG. 4A shows the atomic force microscopy (AFM) counts versus distance plot profile for the triangular structures. FIG. 4B shows the counts versus distance atomic force microscopy (AFM) plot profile for the truncated hopper structures.

The as synthesized gold nanoparticles were studied using X-ray diffraction spectroscopy (XRD). FIG. 5 shows the XRD pattern of the synthesized gold nanoparticles, showing the reflection from the 111 place 2θ of ˜38° . As is evident from the XRD spectrum, the nanoprisms are singly crystalline, whose basal plates surface are atomically flat “111” planes. The functional groups responsible for conversion of nanospheres into nanoprisms were NH and OH groups found in the contents of the red algae extract. FIG. 6 shows the Fourier Transform Infra-Red (FTIR) spectra of Laurencia papillosa extract of the as synthesized gold nanoparticles. FIG. 7 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the gold (Au) atom present in the as-synthesized gold nanoparticles showing the AuO₄F_(5/2) and the AuO₄F₇₇₂ atomic transitions.

As demonstrated above, the invention provides a green, ecofriendly low-cost method for synthesizing gold nanospheres. The nanospheres can be converted into nanoprisms when appropriate concentrations of the red algae, e.g., Laurencia papillosa, is used. The use of eco-friendly sources for the synthesis of gold nanoparticles offers several benefits to the environment and does not involve noxious chemicals. Moreover, the naturally synthesized gold nanoparticles (GNPs) are of great interest in nanoscience for biomedical application specifically for clinical diagnostic applications. GNPs, especially gold nanoprisms, represent a new, advanced tool to study cell function and are useful in optoelectronics and in drug delivery systems to control plant viruses.

It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims. 

We claim:
 1. A method of synthesizing gold nanoparticles using red algae extract comprising: providing a solution of chloroauric acid (HAuCl₄); providing an aqueous solution of red algae extract, and combining the solution of chloroauric acid (HAuCl₄) and the red algae extract solution to produce gold nanoparticles.
 2. The method of synthesizing gold nanoparticles using red algae extract according to
 1. , wherein the red algae extract comprises an extract of Laurencia papillosa.
 3. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein the solution of chloroauric acid (HAuCl₄) includes a chloroauric acid (HAuCl₄) concentration of about 0.25 mM to 5.0 mM.
 4. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein the gold nanoparticles include gold nanospheres.
 5. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein a concentration of the red algae extract is from about 0.01 to about 0.10 g/mol.
 6. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein the gold nanoparticles have a mean diameter in the range of from about 1 to about 100 nm.
 7. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein the gold nanoparticles have a mean diameter in the range of from about 1 to about 55 nm.
 8. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein a shape of the nanoparticles is at least one of spherical, spheroidal, elongated spherical, rod-shaped, and prismatic.
 9. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein the nanoparticles are nanoprisms.
 10. The method of synthesizing gold nanoparticles using red algae extract according to claim 1, wherein the extract of red algae is prepared by a method including the steps of: pulverizing a quantity of dried red algae samples into small pieces; boiling the pieces in water for about 5 minutes to about 10 minutes to provide a boiled extract solution; and isolating the extract from the solution.
 11. The method of synthesizing gold nanoparticles using red algae extract according to claim 10, wherein the red algae is Laurencia papillosa.
 12. The method of synthesizing gold nanoparticles using red algae according to claim 11, wherein the extract is isolated by centrifugation at about 5000 rpm for about five minutes at a temperature of about 5° C. 